From the prior art hybrid vehicles comprising a hybrid drive are known. Besides the internal combustion engine they comprise at least one electric motor or electric machine. In serial hybrid vehicles a generator supplies electrical energy to the electric motor that drives the wheels. In addition parallel hybrid vehicles are known, in which the torques of the internal combustion engine and of at least one electric machine that can be connected to the internal combustion engine are added. In this case the electric machines can be connected to the belt drive or to the crankshaft of the internal combustion engine. The torques produced by the internal combustion engine and/or the at least one electric machine are transmitted to the driven axle by a downstream transmission.
For example, known from DE 102006019679 A1 is a drivetrain with an electrically controllable hybrid drive and an electro-hydraulic control system, a number of electric power units and a number of torque transmission mechanisms. In this case the torque transmission mechanisms can be selectively engaged by the electro-hydraulic control system to produce four forward gears, a neutral condition, an electric operating mode with low and high rotation speeds, an electrically adjustable operating mode with low and high rotation speeds, and an uphill operating mode.
From DE 102005057607 B3 a hybrid drive for vehicles is known, which comprises at least a main motor, in particular an internal combustion engine, a generator, an electric motor and a planetary transmission comprising a sun gear, an ring gear, a planetary gear carrier and planetary gearwheels, which has at least one drive output shaft. In this case it is provided that for a first driving range of the vehicle, in order to add the torques, the driveshafts of the main motor and of the electric motor are coupled to the sun gear of the planetary transmission, and for a further driving range one of the two motors can be coupled by frictional means to the ring gear of the planetary transmission for the mechanical addition of the rotation speeds in accordance with the superimposition principle.
In a shift under load carried out according to the prior art the speed adaptation of the motor required for synchronization to the new gear takes place with the help of the shift elements involved and by action upon the motor torque.
For example, in a traction upshift the transmission capacity of the shift element to be engaged is first increased in order to take up the load and at the same time the transmission capacity of the shift element to be disengaged is reduced, and when the load has been taken up by the shift element being engaged, the speed of the motor is adapted with the help of the shift elements and by action upon the engine torque. In a purely electric load shift the speed of the electric machine is adapted; furthermore, the action upon the torque is carried out at the electric machine. Then, the shift element being disengaged is disengaged completely and the shift element being engaged is engaged completely.
According to the prior art, during such load shifts the electric machine remains torque-controlled during the shift, with specification of a nominal drive torque, and the action upon the torque is performed by the shift sequence control means.